1. Field of the Invention
The present invention relates to a resonator which is provided to an intake flow path of an automobile and reduces intake noise.
2. Description of the Related Art
A resonator utilizing Helmholtz's principle of resonance is disposed in an intake flow path of an engine or an intake flow path of an air conditioning system of an automobile so as to absorb noise generated by gas passing through the flow path. The intake noise at a specific frequency is, thus, absorbed by the resonator.
The resonator is disposed in, for example, an air pipe connecting an air cleaner and a throttle body of the automobile. The resonator has a structure in which an intake flow path of the air pipe communicates with the resonance chamber in a state in which a resonance chamber formed by positively joining an upper case and a lower case to each other is joined to an air pipe. On an air cleaner side of the air pipe, a bellows portion for absorbing vibration is provided. The air pipe is produced by using a polypropylene resin so as to ensure formability of the bellows portion and flexibility of a throttle valve inserting portion. Because air leakage is not permitted in a joint between the air pipe and the resonance chamber of the resonator, the polypropylene resin which exhibits excellent sealing capability and is the same as the material of the air pipe is used for molding the upper case. The polypropylene resin is also used for the lower case because the lower case is integrally fused to the upper case.
Because the air pipe of the automobile is for ventilating a throttle body from the air cleaner, the air pipe is normally disposed in an engine room and it is possible that the air pipe is laid to overstride an exhaust manifold in the engine room in some cases. In such cases, there is a problem concerning heat resistance of the polypropylene resin which constitutes the resonance chamber of the resonator. A maximum resistible temperature of the polypropylene resin is around 120.degree. C. in general, and a heat insulator may be attached to the exhaust manifold or the resonator itself for heat insulation if the temperature exceeds the maximum resistible temperature.
However, in regard to the case of attaching the heat insulator to the exhaust manifold, since the countermeasure against heat of the exhaust manifold has been taken with the aid of improved performance of the engine, the heat insulator has been detached from the exhaust manifold in recent years.
In the case of attaching the heat insulator to the resonator itself, on the other hand, as the heat insulator, bolts, nuts, heat-insulating washers for attaching the heat insulator to the resonator are required, the number of required parts and the assembly man-hour are increased, leading to the cost increase.